This invention relates to a system for detecting abnormality in the internal pressure of a tire which is arranged to automatically detect an abnormal drop taking place for some reason in the internal air pressure of a tire of a motor vehicle and to have an alarm issued in response to a detection signal to inform the driver or the like of the motor vehicle of the abnormality in the air pressure of the tire.
To prevent accidents, it is important to detect an abnormal drop in the air pressure of tires of a motor vehicle while it is on the run or in repose, or immediately before a start at the latest, and to inform the driver of the abnormal pressure droppage.
However, since a wheel of a motor vehicle or the like is a rotating body, power supply to an abnormal pressure detector which is normally to be disposed within a tire of the wheel is difficult. Although power supply can be effected by means of a battery or the like, it is not easy to replace the battery. Besides, it is also difficult to obtain information from such an abnormal pressure detecting means through wiring connection. In addition to that, there is another problem that noises produced by the engine of the motor vehicle and broadcasting radio waves coming from outside to be strongly received tend to make perception of an abnormality detection signal difficult.